Thermal stability of diffusion barriers for storage-node electrode structures of Si-based memory devices

We examine the thermal stabilities of a variety of diffusion barriers for the storage-node bottom electrode structures of Si-based memory devices in an oxygen ambient condition. For the comparative study, O₂-stuffed sputtered TiN, WN_x and TiCl₄-based TiN deposited by chemical vapor deposition (CVD) and sputtered TiAlN diffusion barriers are used with Pt or Ir electrodes. Among the electrode structures used in this study, the sputter TiAIN barrier/Pt structure shows the best thermal stability, exhibiting neither structural collapse nor surface hillocks at 700 °C in O ₂, and those structures are even stable at 750 °C in a N ₂ ambient. The TiN or WN_x barrier deposited either by using CVD, which has superior film step coverage, or by using the sputtering method with the use Pt electrodes shows early oxidation failure at 500 ∼ 600 °C in O₂. The CVD TiN/Ir structure is stable up to 700 °C with no distinctive oxidation in the barrier or reaction due to inter-diffusion between the Ir electrode and the poly-Si underlayer; however, many surface hillocks are formed on the Ir surfaces above at 600 °C, which is thought be due to surface oxidation of Ir. The excellent thermal stability of the TiAlN barrier/Pt structure during O₂ annealing is thought to be due to the early formation of a very thin AlO_x layer that retards any further oxidation of TiSi₂.